Polydicyclopentadiene (poly-DCPD) is obtained through Ring Opening Metathesis Polymerisation (ROMP) of dicyclopentadiene (DCPD). ‘ROMP reaction’ is a metal carbene catalysed reaction using strained cyclic olefins to produce a wide range of polymers.
Poly-DCPD has excellent impact performance, superior chemical resistance, very low water absorption, very low dielectric constant and a high electrical strength.
Today's commercial DCPD formulations system based on molybdenum and tungsten are processed using Reaction Injection Moulding (RIM).
The tremendous development of stable well-defined ruthenium catalysts opens new possibility for poly-DCPD applications. The formulations based on ruthenium catalysts are no longer limited to RIM but can be potentially used in a variety of thermoset process such as filament winding, pultrusion, roto-moulding, casting, resin infusion.
The robust nature of the ruthenium catalysts allows using reinforcements such as glass fibre, mineral fibre, foaming agents and many types of fillers. The ideal catalyst for ROMP reactions should exhibit decreased activity in the presence of monomer at room temperature, so called latency. The main advantage of latent olefin metathesis catalysts is that it can be mixed with the monomers without concomitant polymerization, which allows for longer handling of the catalyst/monomer mixtures or even storage for longer periods (S. Monsaert, A. M. Lozano Vila, R. Drozdzak, P. Van Der Voort, F. Verpoort, Chemical Society Reviews, 2009, 38, 3360-3372).
Schiff base bearing ruthenium catalysts 1, 2a (Scheme 1), 2d (Scheme 2) have been found to be extremely latent in the presence of DCPD monomer and can be stored in DCPD based formulations for months without significant increase in viscosity.

They also showed a high activity in ROMP of DCPD after chemical activation by Lewis or Brønsted acids such as: chlorosilanes or HCl. (N. Ledoux, B. Allaert, D. Schaubroeck, S. Monsaert, R. Drozdzak, P. Van Der Voort, F. Verpoort Journal of Organometallic Chemistry 2006, 691, 5482-5486. S. Monsaert, N. Ledoux, R. Drozdzak, F. Verpoort, Journal of Polymer Science, Part A: Polymer Chemistry, EP Patent Application No 092905785).
Recently we reported that the presence of the substituents in ortho position in N-aryl ring of salicylaldimine ligand is the main factor determining the catalyst latency of 2a-c in DCPD monomer.

The best of the studied precatalysts 2a after chemical activation by trichlorosilanes offers activity comparable to that of the dichloride systems 4 in ROMP of DCPD, while maintaining very high stability in the monomer solution. Thus, new DCPD formulations based on the precatalysts 2a have been designed as two component systems, where the precatalysts and co-catalyst are dissolved into separated components. The polymerization reaction starts when two components are brought together. Typical working life time of precatalyst 2a/trichlorophenylsilane/DCPD monomer mixture is around 60 seconds at 20° C. The fast polymerization reaction is desirable for casting or RIM process, where short cycle time is usually economically favoured. However the ability to extend the working life becomes very important in the moulding of large parts, where the polymerization reaction should not start before mould is completely filled. The same holds for other processes such us RTM, filament-winding or resin infusion, in which low viscosity of monomer/catalysts mixture is needed in order to allow good penetration of the monomer through fibbers structures. In such cases the suitable working life is between 30 minutes to several hours depending on process and size of moulded parts.
The present invention relates to a method for controlling the initiation rate of the catalytic systems based on the ruthenium salicylaldimine precatalysts in ROMP of DCPD without compromising on thermal and physical properties of the polymer.
Several methods to decrease the initiation efficiency of a metathesis catalyst have been already reported. Significant reduction of the catalyst activity of the first generation catalyst type 3 (Scheme 3) in ROMP reactions was achieved when a gel modification additive such as: electron donors, Lewis bases and nucleophiles were added to the reaction mixture. The gel modification additive was assumed to modify the ligand environment of the catalyst. The amount of the additive used depended on the catalytic activity of the resulting catalyst formed in the reaction with the gel modification additive. In the Table 1 some examples of reported gel modification additives are presented.

TABLE 1Effect of addition of the gel modification additives on workinglife time of the catalysts 3 (Scheme 3) (EP Patent No 0865449)Gel modification Additive contentWorking lifeTemp.Entryadditive(w/w %)time (min)° C.1tricyclopentylphosphine0.11211602tricyclohexylphosphine0.23111843pyridine0.095101453triphenylphosphite0.13no reaction4benzonitrile0.23too fast to measure5furan0.23too fast to measure
The Lewis bases such as phosphites completely suppress the polymerization reaction while other additives such us ethers did not show any significant effect on the polymerization rate. However the complete deactivation of the catalyst is not useful, the ideal retardant should decrease the initiation rate without decreasing physical and thermal properties of the polymer. Only the phosphines and pyridine were found to be the most effective in extending working life times (Woodson Ch. S, Grubbs R. H. EP Patent No 0865449).
Significant reduction of the catalyst activity in ROMP reactions by addition of phosphine to the reaction mixture was reported by Stanford et al. This resulted in the decrease in phosphine ligand dissociation from the catalyst precursor and in lower concentrations of the active species, which cause slower polymerization rates (Stanford, M. S., Love, J. L.; Grubbs, R. H. J. Am. Chem. Soc. 2001, 123, 6543-6554). It has been shown, that one equivalent of PCy3 slows down drastically RCM reaction of diethyl diallylmalonate catalyzed by first generation of Grubbs catalysts 3 to 5% of the initial activity (Dias, E. L.; Nguyen, S. T.; Grubbs, R. H. J. Am. Chem. Soc. 1997, 119, 3887-3897). Strak and co-workers reported that low amounts of 1-methylimidazole significantly slow down the cross metathesis reaction of 1-octene in ionic liquids.
Schanz and co-workers published a procedure that reversibly inhibits the ROMP of cyclooctene (COE) and norbornadiene with catalyst 3 in solution or in bulk with 2 or more equivalents of basic N-donor-ligands such as 1-methylimidazole (MIM) or 4-dimethylaminopyridine (DMAP) (S. J. P′Pool, H-J. Schanz, J. Am. Chem. Soc. 2007, 129, 14200-14212) This complete inhibition was attributed to the formation of a low-active hexacoordinate (N-donor)2Rualkylidene species 5 (Scheme 3). It has been also demonstrated that the second generation Grubbs catalyst 4 can be strongly, but not completely, inhibited by 1-methylimidazole (MIM) even when a large excess is used.
To the best of our knowledge, all literature method describing the use of different additives to control the rate of ROMP reactions lead to modifications of the ligand environment of the catalysts. The influence of type of carbene moiety, nature of donor and anionic ligands, on catalyst performance and thermal stability has been investigated extensively, for the Grubbs first and second generation catalysts 3, 4 (Sanford, M. S.; Love, J. L.; Grubbs, R. H. J. Am. Chem. Soc. 2001, 123, 6543-6554; Dias, E. L.; Nguyen, S. T.; Grubbs, R. H. J. Am. Chem. Soc. 1997, 119, 3887-3897; Ritter, T.; Hejl, A.; Wenzel, A. G.; Funk, T. W.; Grubbs, R. H. Organometallics 2006, 25, 5740-5745).
A different concept has been described for the catalytic systems used in Reaction Injection Moulding (RIM) processes (U.S. Pat. Nos. 4,400,340 and 4,943,621). In such a case a molybdenum or tungsten containing catalyst precursor and an alkyl aluminium compound are in separated monomer streams and after mixing the active catalyst is formed. The stream containing the alkyl aluminium can include a compound such as: ester, ether, ketone, alcohols or phenols which inhibit the formation of the active catalyst. However, once the catalyst is formed the initiation is very fast and the polymerization reaction rate cannot be controlled.
All attempts to decrease the DCPD polymerization rates by adding different types previously described inhibitors in the presence ruthenium salicylaldimine/chlorosilane systems failed. This is attributed to strong N-donor character of the additives like 1-methylimidazole, which act as acid scavengers completely blocking the active catalyst formation. Other Lewis bases like triphenylphosphine, isochinoline, pyrazine gave the retardation of maximum 13 minutes (at 1 w/w %), however only polymers with decreased physical and thermal properties were obtained. Addition of ether, phenol, alcohol, keton or ester did not show any influence on the polymerization rate.
To date no inhibitor for the ROMP of DCPD catalysed by ruthenium salicylaldimine/chlorosilane catalytic system has been reported. Thus, there is a need for an efficient retardant that can allow controlling the polymerization rate and making these catalytic systems suitable for the processes where extended working life of monomer/catalyst mixture is required.